Electromagnetically actuated control valves are widely used in fuel injectors (see U.S. Pat. No. 4,742,964 to Ito et al.), and are also widely utilized in timing fluid and injection fuel metering systems for precisely controlling injection fuel and timing fluid on a pressure-time (P-T) basis as disclosed in U.S. application, Ser. No. 08/208,365 commonly assigned to assignee of the present invention. Precise control of the timing and metering of fuel is necessary to achieve maximum efficiency of the fuel injection system of an internal combustion engine. Accordingly, there exists a need for a simple, low cost control valve that provides the precise control required in the injection fuel metering systems.
These control valves are normally operated by an electronic driver circuit that turns on a high current for a short period of time, and then drops to a lower current for the remainder of the time that the driver circuit is turned on. The flow delivered to the fuel injectors, via the control valves, is a function of the time that the actuator of the control valve is turned on and the pressure drop across the valve.
U.S. Pat. No. 4,982,902 to Knapp et al. discloses an electromagnetically actuatable valve including an actuator portion having an armature with extending tongues which firmly connect a ball with the armature. In addition, a closing spring sits on a side of the ball opposite to a valve seat and biases the ball against the valve seat so as to close the valve seat in the non-excited state of the actuatable valve. The armature, however, is of a thin disc-like form and upon actuation of solenoid coils, rapid movement may result in fluttering movement of the flat armature. This may result in improper seating of the ball on the valve seat, and therefore poor precision in controlling the amount of fuel to be passed to the fuel injectors.
In addition, even though the disclosed armature in Knapp et al. executes a pivotal motion to assure seating of the ball in the valve seat, this pivoting does not ensure a proper seating at precisely the intended point of time and further permits the ball to unintentionally move in a lateral fashion which reduces the likelihood of a clean seating with the valve seat. In addition, the armature has limited contact area with the ball through the tongue portions of the armature. When the valve is excited, the armature rapidly moves to a position in contact with a step portion of the control valve housing that limits movement of the armature. The armature itself, made of sheet metal, is soft and the contact force with the step portion can damage the armature. In addition, when the valve is to be placed in its unexcited (closed) state, the ball rapidly moves to its initial position to seat with the valve seat to dose off fluid flow. The impact force exerted on the ball results in impact force on the armature. The mount of beating on the armature is a function of the contact area with the ball and the force applied. The armature is made of magnetic material and is normally very soft. With little contact area between the tongues of the armature and the ball, a given amount of force will result in high beating, which the soft armature is not able to withstand for an extended period of time. Furthermore, the disclosed system of Knapp et al. is unlikely to be useful in systems that demand that the control valve be used in high pressure circuits because the reference discloses that it is intended for use in low pressure environments.
A further problem existing in Knapp et al., and present control valves generally, is the seat beating that occurs when the control valve is rapidly moved between its open and closed positions. Even though the valve seat is made of a much harder material than the armature, the rapid closing motion of the armature forces the ball to harshly seat against the valve seat, imparting great impact force between the ball and the valve seat, causing both spalling of the ball and seat beating to the valve seat. Both of these problems further reduce the life of the parts of the control valve, and therefore the life of the control valve itself.
U.S. Pat. No. 3,738,578 to Farrell discloses a magnetic armature valve wherein a permanent magnetic armature has a ball welded to the end of the armature. Therein, the ball seats against a conical seat with the aid of a biasing spring acting against the armature. The force that the spring imparts on the armature is adjustable with the movement of a screw in a nut. The reference also discloses that the nut, which is used to limit the travel of the armature, can be adjusted so as to adjust the total travel of the armature. Problems, however, exist with this valve assembly as well. For one, welding the check ball results in deformation of the ball from its purely spherical form, which results in a imprecise seating of the check ball with the conical seat. This improper seating results in poor control over the amount of fuel flowing through the control valve to the assembly to the cylinders of the engine.
In addition, just as with Knapp et al., the conical seat and the check ball must withstand great stress with the high pressure, rapid movement of the check ball against the conical seat to control fuel flow to the cylinders of the engine. This results in rapid deterioration of the conical seat and the check ball due to seat beating and ball spalling, respectively. These problems further exacerbate the problems of improper seating and imprecise fuel flow to the cylinders in addition to limiting the life of the parts themselves.
U.S. Pat. No. 4,946,107 to Hunt discloses an electromagnetic fuel injection valve including a V-shaped notch formed at the exit end of a nozzle of a fuel injector wherein wings of the notch form guide tips. A ball valve, or check ball, is secured in the notch and seats against a cut-out portion of a nozzle seat. This structure, however, is susceptible to many of the problems of the assemblies of the above-noted patents. For instance, the notch portion does not maximize the contact area between the ball valve and the nozzle. Therefore, with a given amount of contact force between the end of the nozzle and the ball valve, force from the contact of the ball valve and the nozzle seat is imparted to the nozzle (made of a soft material) which causes beating of the nozzle and can easily damage the nozzle, thereby shortening the life of the injector.
Furthermore, because the notch portions do not to cross the major diameter of the ball valve, the ball valve must be welded to the notch portions. If this is the case, then the problem of ball deformation occurs, as discussed above. If an adhesive substance is used to secure the ball to the notch portions, this can alter the positioning of the ball valve so as to improperly seat in the nozzle seat even if a very thin layer of adhesive is used.
U.S. Pat. Nos. 5,222,673 to Reiter and 5,255,855 to Maier et al. both disclose fuel injection valves wherein the fuel injection valve includes an armature that biases a ball-shaped valve closing body toward a valve seat. When a magnetic coil is energized and the armature is moved to its excited position, the ball-shaped valve closing body comes into contact with a stop pin so as to limit the movement of the ball-shaped valve closing body.
Many of the previously-noted problems also exist with this structure. First, the armature contacts the ball-shaped valve body in a limited amount of area, which means that a great amount of force is placed on the armature because of the impact force experienced when the ball-shaped valve body contacts the valve seat. The soft armature experiences deformation quickly, shortening its useful life. In addition, when the ball-shaped valve body is lifted from the valve seat and its movement is limited by contact with the stop pin, a great amount of impact force generated by the contact of the stop pin and the ball-shaped valve body causes pin beating and ball spalling. Even though the underside of the stop pin, which is what the ball-shaped valve body contacts, is made of a hardened material in Reiter and Maier et al., this does not prevent pin beating, which leads to deformation or cracking of the stop pin. All of these problems result in improper fluid flow control and a shortened life of the fuel injector.
Therefore, there still exists a need for a simple, low cost control valve that minimizes the problems of armature deformation, pin beating, ball spalling, and seat beating without compromising the precise control necessary in a timing fluid and injection fuel metering system.